Waves and Tidal Flat Ecosystems

The authors explain and describe the mutually rewarding insights that resulted from the interdisciplinary collaboration between an environmental study group working coastal ecosystems and effects of oil spills and applied mathematicians modelling wave motion on sandy beaches. By using the unified Navier-Stokes equations with a Bingham fluid model for spilled oil, multi-phase flow analysis were made. Decomposition of spilled oil by bacteria was simulated as a chemical reaction, and the theoretical and numerical analysis suggested a countermeasure to help reduce stress on coastal ecosystems. The new understanding of how the ecosystems both depend upon, and help to determine, the nature of the shoreline demonstrates promising ways to better assist and exploit the regenerative powers inherent in nature.

Eiichi Baba is Professor, Graduate School of Engineering, Hiroshima University, Japan; and Professor, Director of Information Exchange Office, Hiroshima University, Japan.

What is a tidal flat?

1

(22)

Introduction

1

(1)

Function and structure of natural and man-made tidal flats

2

(8)

Pysico-chemical characteristics

2

(3)

Hydraulic characteristics

5

(1)

Biomass of bacteria and macrobenthos

5

(3)

Respiration rates of microorganisms

8

(1)

Discussion

8

(2)

Key factors to determine a tidal flat characteristic

10

(5)

Transfer experiments

10

(2)

Relationship between silt content and bacterial population

12

(3)

Fluid flow on a tidal flat

15

(8)

Outline of study sites

15

(1)

Shear stress

16

(2)

Sedimentation of sand

18

(2)

Discussion

20

(3)

Effects of waves and tide on tidal flat ecosystems

23

(18)

Introduction

23

(1)

Method of experiments on internal flow in seabed

24

(2)

Flow visualization inside sandy beach

24

(1)

Wave and tide control

25

(1)

Quantification of seawater infiltration in sandy beach

25

(1)

Role of wave and tide on seawater infiltration in sandy beach

26

(3)

Fresh seawater infiltration

26

(2)

Silt movement by wave action

28

(1)

Role of wave and tide on ecosystems in tidal flats

29

(9)

Measurement of seawater infiltration in tidal flat

29

(3)

Observation of benthic organisms in tidal flat simulators

32

(6)

Concluding remarks

38

(3)

Unified model for wave breaking action

41

(12)

Introduction

41

(1)

Mathematical model

42

(4)

Notations and geometry

42

(2)

Conservation of mass for total flow system

44

(1)

Conservation of momentum for total flow system

44

(1)

Surface blocking effect to seawater due to accumulated materials on the beach

45

(1)

Unified model for two-phase flow with surface blocking effect

46

(1)

Numerical results

47

(6)

Correlation between wave breaking action on a sloping beach and internal flow of a sandy beach

47

(1)

Flow pattern and infiltration area of seawater in sandy beach

48

(2)

Time averaged flow under the beach

50

(1)

Surface blocking effect to seawater

51

(2)

Oil pollution: human damages on hydraulic regime in sandy beach ecosystems

53

(18)

Introduction

53

(1)

Infiltration of stranded oils into sandy beach sediments by waves and tides

54

(11)

Waves and Tides

54

(3)

Volume of stranded oils

57

(1)

Tidal Cycles and temperature

57

(1)

Viscosity of oil

58

(2)

Weathered and dispersed oils

60

(5)

Effects of the penetrated oils into sandy beach sediments on seawater infiltration by waves

65

(6)

Theoretical study of oil pollution

71

(22)

Introduction

71

(1)

Behavior of spilled oil in the surfzone

71

(1)

Mathematical model

72

(4)

Notations and geometry

72

(1)

Conservation of mass for a total flow system

73

(1)

Conservation of momentum for a total flow system

74

(1)

Unified equations of motion for a three-phase flow

75

(1)

Adhesive phenomena of oil on a sandy beach

76

(1)

Unified model for three-phase flow with adhesion

76

(2)

Numerical results

78

(15)

Process of drifting ashore of spilled oil

78

(3)

Deformation of oil

81

(1)

Adhesion and sliding phenomena between oil and water in a sandy beach

81

(5)

Infiltration phenomena of oil into a tidal flat or sea bed due to the tidal motion

86

(1)

Blocking effect by penetrated oil on the internal flow in sand

86

(7)

Oil pollution: human damage on hydraulic regime and benthic communities in tidal flat ecosystems

93

(16)

Introduction

93

(2)

Penetration of stranded oils into tidal flat sediments by tides

95

(2)

Effects of the penetrated oils into tidal flat sediments on seawater infiltration by tides

97

(3)

Effects of oil spill on seawater infiltration and macrobenthic community in tidal flats

100

(9)

introduction

100

(1)

The tidal flat simulator

101

(4)

Effects of oil spill on tidal flat ecosystem

105

(1)

Macrobenthic community

106

(3)

Decomposition mechanism of spilled oil by bacteria

109

(8)

Introduction

109

(1)

Notations

109

(1)

Characteristics of oil decomposition into water

110

(1)

Reactivity condition

111

(1)

Incompressibility condition for a total flow system

111

(1)

Biological contribution to satisfy reactivity condition

112

(1)

Unified model for three-phase flow with decomposition

113

(1)

Numerical results

114

(3)

Breaking waves and ecosystem dynamics

117

(10)

Introduction

117

(1)

Mathematical modeling

117

(4)

Mathematical description of aeration due to breaking waves

117

(3)

Modeling for ecosystem dynamics

120

(1)

Coupling scheme between waves and ecosystem dynamics

121

(1)

Numerical results

122

(5)

Aeration due to breaking waves

122

(1)

Simulation of ecosystem dynamics

122

(5)

Methodologies for theoretical studies

127

(1)

Introduction

127

(1)

Mathematical methodologies

127

(1)

Distribution theoretic approach to multi-phase flow

127

(7)

Anti-smearing device for numerical free surface

134

(1)

Numerical methodologies

135

(1)

Discretized model for the total system

135

(2)

Two-phase free surface flow with large density difference

137

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